Method and System for Configuring a Communication Network, Related Network and Computer Program Product

ABSTRACT

An antenna site equipped with reconfigurable antennas in a communication network and having capacity to serve communication traffic in a respective area of competence is configured by partitioning the area the area of competence into a set of cells. The number of cells in the set is optimized by ensuring that the traffic is evenly distributed among the cells. This result is preferably achieved starting from a reference set of cells by locating: —i) areas of superposition between adjacent cells covered jointly by traffic capacity of adjacent cells in the reference set of cells, and—ii) uncovered areas between adjacent cells, that is, areas not covered by traffic capacity of any cells in the reference set of cells. The areas of superposition are removed and the traffic capacity thus made available is assigned to the uncovered areas. If any uncovered areas remain, the number of cells in the reference set of cells is increased and the process repeated. If no uncovered areas between adjacent cells are located, the possibility exists of decreasing the number of cells in the reference set of cells and the process is repeated to check whether the area of competence can be properly covered with a lower number of cells.

FIELD OF THE INVENTION

The invention refers to the configuration of communication networks.

The invention was developed with specific attention paid to its possibleuse in the optimization of second and/or third generation mobilecommunication networks using reconfigurable antennas. Reference to thispreferred field of use is not however to be construed in a limitingsense of the scope of the invention.

DESCRIPTION OF THE RELATED ART

Reconfigurable antennas (i.e. antennas adapted to modify their radiationpattern characteristics) represent a powerful tool for improvingperformance of the radio access portion of mobile telecommunicationnetworks. This applies both to the extension of coverage area and tocapacity, that is the number of users for which service is guaranteed.

Research in the area of telecommunications and related technologicaldevelopment over the recent years has led to the possibility ofdesigning and manufacturing various types of reconfigurable radiatingsystems. Specifically, in addition to conventional antennas—that areessentially “passive” components—electrically controllable antennas arenow available for communication systems, especially for use as basestations in mobile telecommunication systems. So far, the availabilityof these “reconfigurable” antennas (typically in the form of so-calledphased-array antennas) has been exploited primarily with a view toadapting the antenna characteristics to the requirements of networkplanning, this while dispensing, inasmuch as possible, with the need ofdirect interventions at the antenna site when the antennacharacteristics need to be modified.

For instance, WO-A-2005/004515 discloses a communication networkincluding a plurality of antennas which is configured by including amongthe antennas at least one reconfigurable antenna adapted to servecommunication traffic in a respective coverage area. The reconfigurableantenna has a radiation diagram exhibiting a plurality of selectivelyadjustable gain values for a set of directions, wherein each directionin the set defines a propagation path between the antenna and a portionof the coverage area. For each direction in the set, at least one valueof communication traffic and at least one attenuation value over thepropagation path are determined. A gain value is then selectively andindependently allotted to each direction in the set as a function of atleast one of the value of communication traffic and the attenuationvalue determined for that direction.

In WO-A-03/045094 an arrangement is disclosed including a statisticalsmart antenna configuration wherein antenna patterns associated withvarious base stations of the communication network are configured bytaking into account the morphology and topology of the service area.Antenna patterns are configured using merit-based determinations basedupon link propagation conditions such as those associated with themorphology and topology of the service area, with the aim of positivelyserving areas which are best served by the network being optimized whilenot serving areas which are best served by other network systems.

OBJECT AND SUMMARY OF THE INVENTION

The Applicants have noted that a need can exist for arrangementsadmitting a higher degree of flexibility in optimizing the number ofcells associated to an antenna site of a communication network.

Specifically, a need is felt for arrangements wherein said optimizationprocess involves the number and the shapes of the radiation diagrams ofreconfigurable antennas equipping the radio base stations (e.g. theantenna “sites”) in the communication network, with a view to reduceinterference and balance the load (offered traffic) for each antennasite.

The object of the invention is thus to provide a satisfactory responseto those needs.

According to the present invention, that object is achieved by means ofa method having the features set forth in the claims that follow. Theinvention also relates to a corresponding system, a related network aswell as a related computer program product, loadable in the memory of atleast one computer and including software code portions for performingthe steps of the method of the invention when the product is run on acomputer. As used herein, reference to such a computer program productis intended to be equivalent to reference to a computer-readable mediumcontaining instructions for controlling a computer system to coordinatethe performance of the method of the invention. Reference to “at leastone computer” is evidently intended to highlight the possibility for thepresent invention to be implemented in a distributed/modular fashion.

The claims are an integral part of the disclosure of the inventionprovided herein.

The Applicant has found that this problems can be solved by a method forconfiguring an antenna site equipped with at least one reconfigurableantenna in a communication network, such as e.g. 2G or 3G mobilecommunications network, wherein the antenna site has capacity to servecommunication traffic in a respective coverage area (area ofcompetence); the coverage area is partitioned into a reference set ofcells, each cell corresponding to a portion of the coverage area overwhich a specific set of radio channels is transmitted or received. Thenumber of cells is optimized by causing an offered traffic to be evenlydistributed among the cells. This result is achieved by checking thecells in the reference set to locate:

i) areas of superposition between adjacent cells, i.e. areas coveredjointly by traffic capacity of adjacent cells in the reference set ofcells, and

ii) uncovered areas between adjacent cells, i.e., areas not covered bytraffic capacity of any cell in said reference set of cells.

The areas of superposition are removed, so that traffic capacity is madeavailable from either of the adjacent cells that gave rise tosuperposition. This traffic capacity is assigned to the uncovered areas.If any uncovered areas remain at the end of the process, the number ofcells in the reference set is increased and the process is repeated inan iterative way. If no uncovered areas between adjacent cells arelocated, the number of cells in the reference set is reduced in order toascertain whether adequate coverage can be assured with a lower numberof cells.

In a preferred aspect the arrangements described herein, afterdetermining the number of cells, associates a radiation diagram (in thehorizontal direction H and in the vertical direction V) to each celle.g. by resorting to the arrangement disclosed for example inWO-A-2005/004515.

In a further preferred aspect the information concerning the number ofcells and the related radiation diagrams can be sent to a control unitwhich controls at least one reconfigurable antenna of the antenna site,said reconfigurable antenna comprising a plurality of radiatingelements. For each cell associated with the at least one reconfigurableantenna, the control unit produces a related radiation diagram bymodifying amplitudes and phases of the signals transmitted or receivedthrough the radiating elements of the reconfigurable antenna.

Essentially, the arrangement described optimizes the number and theshapes of the cells and of the related radiation diagrams of thereconfigurable antenna(s) equipping an antenna site on the basis of anumber of factors: these typically include both the propagationcharacteristics of the antenna site and the offered traffic levels inthe coverage areas associated to the site.

As a result, interference can be reduced and the load (offered traffic)for each site properly balanced in order to reduce the probability ofblock/congestion.

BRIEF DESCRIPTION OF THE ANNEXED REPRESENTATIONS

The invention will now be described, by way of example only, withreference to the enclosed representations, wherein:

FIG. 1 is a flowchart representative of certain processing stepsperformed within the framework of the arrangement described herein;

FIG. 2 is a schematic pictorial representation of a possible scenario ofapplication of the arrangement described herein;

FIG. 3 is a schematic representation of processing of informationrelated to each cell or sector within the framework of the arrangementdescribed herein;

FIG. 4 is another flowchart representative of certain processing stepsperformed within the framework of the arrangement described herein:

FIGS. 3 to 12 are graphical representations of various subsequentprocessing steps performed within the framework of the arrangementdescribed herein;

FIGS. 13 to 15 are representative of certain entities involved in thevarious steps of FIGS. 3 to 12; and

FIG. 16 is a block diagram representation of a possible embodiment of asystem as described herein.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The arrangement (method and system) described herein is adapted for usein optimizing a communication network (generally a mobile communicationnetwork, even though use in connection with e.g. a Wireless Local AreaNetwork—WLAN can be contemplated) including at least one reconfigurableantenna: see reference 70 in the block diagram of FIG. 16. For directreference, the following description will assume, by way of non-limitingexample, that each reconfigurable antenna k is comprised of an array ofN_(k)×M_(k) elements.

The method and system described herein uses as a first input adescription of the network indicating the presence and location of thesites equipped with reconfigurable antennas: it will be appreciated thatthese “reconfigurable sites” may represent just a portion of the sitesin the network.

Such a description of the network may be a file in tabular formcontaining, for each of the sites in the network, a set of items ofinformation such as, e.g.:

the location of the site in geographical coordinates (latitude,longitude);

a Boolean variable that indicates whether the site is reconfigurable ornot (1 is for instance the value for reconfigurable site and 0 for notreconfigurable site);

the number of antennas installed at the site;

the pointing of each antenna (tilt and azimuth); and

the input power to each antenna.

Typically, the radiation diagram of each antenna is represented, in amanner known per se, as a pair of vectors representative of the crosssections of the radiation diagram in the horizontal plane (H) and thevertical plane (V). The three-dimensional diagram can be reconstructedfrom the H/V sections, for instance as described in U.S. Pat. No.6,903,701.

A second input to the method and system described herein is a structuredset of territorial data stored in a data base (not shown in thefigures). Specifically, the territory is discretized in elementary areascalled “pixels” (see for instance FIG. 3, to be described in greaterdetail in the following) and the territorial data are stored in thedatabase. This occurs preferably in the form of matrixes and/or vectors,but reference to this specific arrangement should not be construed in alimiting sense of the scope of the invention. In such a matrixorganization of the territorial data each individual element in a matrixis associated to a particular pixel and contains the numerical value ofa corresponding territorial attribute. For instance, the territorialdata may include:

a traffic matrix whose elements are representative of the values of thetraffic expected for a given service in the respective pixels in a“sector”;

a matrix of altitudes, whose elements are representative of the valuesof the (average) altitude over sea level of the respective pixels;

a morphology matrix, whose elements are indicative of the morphologiesof the respective pixels, in that these values are representative ofcodes each associated with one morphological characteristic or featureof the respective the pixel (e.g.: thick wood, thin wood, orchard,vegetated agricultural area, uncultivated area, barren area, etc.); and

a building matrix, whose elements are representative of the percentagesof building present in the respective pixels.

A third input to the method and system described herein is a set of theparameters included in a configuration file. These parameters will bedescribed in detail in the following.

Turning now specifically to the flow chart of FIG. 1, starting from a“START” step and ending with an “END” step, the method and systemdescribed herein define for each of the reconfigurable sites in thenetwork:

an area of competence of the reconfigurable site (step 100);

an optimum number of cells associated to the reconfigurable site and theoptimum angular amplitudes of the various sectors associated therewith(step 102);

an optimum radiation diagram on the vertical (V) plane (step 104); and

an optimum radiation diagram on the horizontal (H) plane.

For the purpose of the present invention, a cell is defined as a portionof the coverage area over which a specific set of radio channels istransmitted or received. Typically, a cell is associated with anidentification or pilot channel. In particular, in current second andthird generation networks an identification or pilot channel (e.g. aBroadcast Control CHannel or BCCH for 2nd generation networks or aCommon Pilot CHannel or CPICH for 3rd generation networks) is associatedwith each cell.

The related optimization process operates independently for each site.Consequently, an explicit indication of the site involved will beomitted throughout the rest of this description.

As indicated, the step 100 involves the definition of an area ofcompetence of the reconfigurable site. As used herein, the designation“area of competence” designates a portion of the territory covered bythe network wherein a certain service is expected to be guaranteed bymeans of a given site.

Typically, the areas of competence of the different sites are identifiedas described in the following.

The radiation diagrams corresponding to the antennas alreadyinstalled/planned for the non-reconfigurable sites are first considered,on a cell-by-cell basis. For each such cell a corresponding value oftransmission power is defined in the configuration file supplied as aninput to the method and system described herein.

Conversely, for the reconfigurable sites a reference configuration isconsidered which is comprised of N cells each associated with a relatedradiation diagram. In a presently preferred embodiment N=1 and anisotropic diagram is assumed. A power level P_(ISO) is associated tosuch an isotropic diagram based on the following relationship:

P _(ISO) =G _(AR) *P _(AVE)

where:

G_(AR) is the average gain expected for reconfigurable antenna,

P_(AVE) is the average power level over the power levels associated tothe site antennas, which are known from the network description file.

Starting from such radiation diagrams, “field” matrixes are calculatedfor each cell. These matrixes provide, for each pixel (m, n) in the areaconsidered, an estimate of the field received in the pixel as a functionof the transmitted power level associated to the cell considered.

In order to reduce computational time and occupation of memory, thecalculation can be limited, for each cell, to the pixels included in anarea limited in terms of the maximum distance from the site (i.e. theradio base station) to which the cell is associated. The electricalfield can computed by resorting e.g. to the method described in G.Bussolino, R. Lanzo, M. Perucca “RASPUTIN: a field strength predictionmodel for large and small mobile cell system using territorial databases”, 7th International Network Planning Symposium, Sidney 1996.

The area of competence of a reconfigurable site (say “X”) can bedetermined as the set of those pixels (m, n) that satisfy the followingrequirements:

the field received at the pixel (m, n) from the isotropic antennaassociated with the reconfigurable site X is higher than the fieldsreceived from cells associated with other sites of the network;

the field received at the pixel (m, n) from the isotropic antennaassociated with the reconfigurable site X is higher than a minimumthreshold E_(min); this threshold is defined, for instance, byconsidering an adequate safety margin with respect to the sensitivity ofthe mobile terminals; in turn this is defined by the related technologystandards as the minimum power that allows the correct demodulation anddecoding of the signal received in the presence of thermal noise.

A minimum power threshold can be calculated, e.g., on the basis of thefollowing relationship:

P _(min) =S _(MS) +M

where S_(MS) represents the sensitivity of the terminal and M is asafety margin currently applied in planning.

According to known criteria, the minimum field threshold E_(min) canderived from the minimum power threshold P_(min) by means of thefollowing relationship:

E _(min) =P _(min)+77.2+20·log(f)−G _(MS)

where f is the operating frequency (in MHz) and G_(MS) the gain of theantenna of the mobile terminal: this is typically considered equal to 0dB for the purpose of calculating the minimum field threshold.

The area of competence for the site X (designated A in FIG. 2, where theneighboring sites are generally designated Y1, Y2, Y3, and Y4) is thenpartitioned into elementary sectors of constant angular amplitude: sucha partitioning process takes place in the horizontal plane.

These elementary sectors represent elementary units that are thenaggregated (as better detailed in the following) in sets to form angularsectors of wider amplitude. Each of these wider sectors, whose widthsdepend on the number of elementary sectors forming them, represents a“cell” served by a reconfigurable antenna (step 102).

For the sake of simplicity, the amplitude of eachindividual—elementary—sector (and, accordingly, the number of suchsectors for site) is selected as a constant value for all the sitesconsidered sites. This constant value is determined as a function of thedimensions of the area of competence A and the spatial resolution (i.e.the dimensions of the pixels) adopted.

Typical values for the angular amplitude of the elementary sectors arein the range of 5 to 20 degrees. Of course, these values are in no waybinding. Similarly, for reasons of practicality (and, again, withoutthis being in any way imperative for the invention) the amplitude of theangular sectors is chosen as an integer submultiple of 360°.

If the angular amplitude of the elementary sectors is denoted ω, thepartitioning process operates in the following way. Starting from theangle “0” which corresponds to the “North” direction, the firstelementary sector corresponds to the angular sector between 0 and ω. Thesecond elementary sector corresponds to the angular sector between w and2 w and so on, until the whole angle of 360° is covered.

The following entities are then computed for each of the reconfigurablesites and each of the elementary sectors that make up the related areasof competence:

the number of pixel, calculated by including all the pixels whose centerbelongs to the elementary sector;

the offered traffic, calculated by adding the traffic present in thepixels belonging to the elementary sector considered. The case of asingle service (e.g. voice calls) will be considered herein for the sakeof simplicity of the description without any limiting effect on theinvention. Multi-service scenarios can be handled e.g. by defining anequivalent “single service” traffic based on the following relationship:

$T_{eq} = {\frac{1}{R_{1}}{\sum\limits_{i = 1}^{N_{serv}}{T_{i} \cdot R_{i}}}}$

where T_(i) and R_(i) respectively denote the traffic (in Erl) and thebitrate (in kbit/s) associated with a given service i. R₁ denotes thebitrate of a first service, taken arbitrarily as a reference;

the representative attenuation of the elementary sector (see FIG. 3),i.e. the maximum attenuation A, calculated on a set of pixels (definedstarting from the pixel(s) having the lowest values of attenuation) thatcollect a given percentage Th_(comp) (for instance Th_(comp)=95%) of thewhole traffic t_(tot) on the elementary sector. The attenuation valuescan be calculated for each pixels belonging to an elementary sector fromthe values of electric field, based on the following relationship:

A(m,n)=P _(ISO) −E(m,n)+77.2+20·log(f)

where P_(ISO) represents the reference power used for the definition ofthe competence area of the considered site, E(m,n) represents the fieldreceived at the pixel (m, n) from the isotropic antenna and f is theoperating frequency in MHz;

maximum distance, corresponding to the distance between the site and thecenter of the pixel farthest away from the site among those that wereused to define the representative attenuation of the sector. Thedistance is calculated in plane coordinates UTM.

In brief, the step 102 of the optimization process described in thefollowing has the aim of defining the optimum number of cells associatedto the site and the optimum angular amplitude of the different cells.

The main result of such a step is, for each reconfigurable antenna kconsidered, the definition of an optimum number N_(cell)(k) of cells tobe associated to that antenna. For each reconfigurable antenna k,φ_(az)(k) will denote the mechanical azimuth derived from the networkdescription file. In the following the notation (k,j) will indicate thecell j associated to the reconfigurable antenna k.

For each such cell, the optimization process yields as an output thefollowing entities, all of which are expressed as integer multiples ofthe amplitude of the elementary sector (ω):

Δ(k,j): angular amplitude of the cell (k,j);

φ_(start)(k,j): angle at which the cell (k,j) begins;

φ_(stop)(k,j): angle at which the cell (k,j) ends;

T(k,j): traffic offered in the cell (k,j).

For each reconfigurable antenna k, the pair of indexes (k, 1) denotesthe cell that contains the azimuth φ_(az)(k) of the antenna. Thefollowing control variables are then defined whose values, equal for allthe cells belonging to the reconfigurable site, represent furtherconfiguration parameters for the optimization process described herein:

Δ_(max): maximum angular amplitude of the cells;

δ_(az): maximum angular distance between azimuth (corresponding e.g. tothe pointing direction in the horizontal plane of the panel thatconstitutes the reconfigurable antenna) and the cell boundaries, definedby the angles φ_(start)(k,j) and φ_(stop)(k,j) at which the cell (k,j)starts and ends, respectively.

Again, the angular values above are expressed as integer multiples ofthe amplitude of the elementary sector (ω). Possible values for Δ_(max)and δ_(az) are 130° and 70°, respectively.

An object of the arrangement described herein lies in determining foreach reconfigurable antenna k and, therefore, for each mechanicalazimuth φ_(az)(k), the optimum number N_(cell)(k) of cells to associateto that antenna.

The total number of cells associated to a given reconfigurable site willthus be determined as:

$N_{cell}^{tot} = {\sum\limits_{k = 1}^{N_{RA}}{N_{cell}(k)}}$

where N_(RA) is the number of reconfigurable antennas associated withthe site, which can be derived from the description file of the network.

The optimization process described herein aims at achieving loadbalancing, namely distributing as evenly (i.e. uniformly) as possiblethe traffic offered by the different cells of the site, by making it asclose as possible to a target value. In a presently preferredembodiment, the target value T_(target) is defined as:

$T_{target} = \frac{T_{tot}}{N_{cell}^{tot}}$

where T_(tot) denotes the total traffic in the area of competence of thesite.

In additionally to the target value, the optimization process considersa maximum value of traffic T_(max) that can be borne by a single cell.This value can be estimated in operation depending on the networktechnology involved. For instance, for second generation mobilecommunication networks, the value for T_(max) can be derived from thenumber of channels assigned to the cell. For third generation mobilecommunication networks, the value for T_(max) can be derived via polecapacity analysis (see, for instance: “WCDMA for UMTS”, edited by H.Holma and A. Toskala, Wiley, pp. 191-193).

A significant feature of the optimization process described herein liesin that it provides a way of estimating, and thus optimizing, the numberof cells associated to reconfigurable antennas as well as the angularamplitude of each of said cells.

This result is achieved in an iterative way as better represented by theflow chart of FIG. 4. The iterations of FIG. 4 do not require anymodifications in the values previously set for T_(tot) and T_(max) andare usually started by setting N_(cell)(k)=1 for all the reconfigurableantennas while hypothesizing a maximum value for N_(cell)(k) equal to,e.g., 4.

The flow chart of FIG. 4 again involves a START step and a STOP stepplus a number of steps 200 to 208 therebetween as described in thefollowing. Specifically, the blocks 200, 202, and 204 correspond tosteps designated: “cell construction”, “overlap management” (i.e.removing superpositions between adjacent cells) and “intercell spacemanagement” (i.e. avoiding that uncovered areas may remain betweenadjacent cells).

In the cell construction step 200, given a reconfigurable antenna k, theamplitudes of the cells are defined as sums of elementary angularsectors. The corresponding number of cells N_(cell)(k) (herehypothesized to range from 1 to 4) as well as the target trafficT_(target) deriving therefrom according to the relationship previouslyillustrated are calculated until any of the following criteria is met:

T(k,j)>T _(target) (i.e. the target load for the cell is reached);

T(k,j)>T _(max) (i.e. the maximum load for the cell is reached);

Δ(k,j)=φ_(stop)(k,j)−φ_(start)(k,j)>Δ_(max) (i.e. the maximum amplitudeor width for the cell is reached;

φ_(stop)(k,j)−φ_(az)(k)>δ_(az) and φ_(az)(k)−φ_(start)(k,j)>δ_(az)

(i.e. the maximum angular distance from the mechanical azimuth of theantenna is reached).

Angular entities are expressed in terms of number of elementary sectors.

The iterative procedure begins by setting N_(cell)(k)=1. Subsequently,the value of N_(cell)(k) can be increased as a result of the “intercellspace management” step 204 described in the following.

The following description (which refers to FIGS. 5 to 8) details thesector analysis underlying the cell construction process in fourdistinct situations as identified by the number of cells of thereconfigurable antenna (namely N_(cell)(k) equal to 1, 2, 3, and 4,respectively).

N_(cell)(k)=1 (FIG. 5)

The first elementary sector of the only cell is the one containing theazimuth φ_(az)(k); elementary sectors are then added on both sides e.g.by proceeding clockwise and counterclockwise beginning from theelementary sector containing φ_(az)(k), until one of the conditions forcell completion listed above is met.

N_(cell)(k)=2 (FIG. 6)

The cell (k,1) is constructed starting from the elementary sector thatcontains the azimuth φ_(az)(k) by adding elementary sectorscounterclockwise until one of the conditions for cell completion listedabove is met; the cell (k,2) it is constructed similarly by proceedingclockwise starting from the elementary sector that is “clockwise”adjacent to the cell (k,1) that contains the azimuth φ_(az)(k) byadding, always in a clockwise direction, new elementary sectors untilone of the conditions for cell completion listed above is met.

N_(cell)(k)=3 (FIG. 7)

The cell (k,1) is constructed as in the case where N_(cell)(k)=1, thatis by adding elementary sectors alternatively clockwise andcounterclockwise starting from the elementary sector containing theazimuth φ_(az)(k) until one of the conditions for cell completion listedabove is met. The cell (k,2) and the cell (k,3) they are constructed byproceeding, respectively, clockwise starting from the elementary sectorthat is “clockwise” adjacent to the cell (k,1) and counterclockwisebeginning starting from the elementary sector that is “counterclockwise”adjacent to the cell (k,1), in both cases until one of the conditionsfor cell completion listed above is met.

N_(cell)(k)=4 (FIG. 8)

The cell (k,1) and the cell (k,3) are constructed proceedingcounterclockwise in the aggregation of the elementary sectors, while thecell (k,2) and the cell (k,4) are constructed proceeding clockwise untilone of the conditions for cell completion listed above is met.

The sector analysis for the determination of the optimum amplitude to beassigned to the cell is applied independently for each reconfigurableantenna of the site. The first step typically involves hypothesizing asingle cell for each reconfigurable antenna.

If, for instance, a reconfigurable site equipped with threereconfigurable antennas is considered, at the end of the first step ofthe optimization process a situation will generally occur similar to theone illustrated in FIG. 9, involving both areas (comprised of one ormore elementary sectors) giving rise to superposition (overlap) withcells belonging to different antennas and areas (again notionallycomprised of one or more elementary sectors) that are left uncovered inthat they are not reached by any of the cells constructed, thus givingrise to “intercell spaces”

In the following, traffic offered to elementary sectors that belong toan overlap/superposition will be designated “superposition traffic”,while the traffic (notionally) offered to those elementary sectors thatbelong to a intercell space will be designated “uncovered (intercell)traffic.”

In the presently preferred embodiment of the arrangement describedherein, the following formalism is adopted for representing thesuperposition traffic and the uncovered traffic:

T_(superp)[(k,j) (k′,j′)] will denote the superposition traffic betweenthe cell j of the reconfigurable antenna k and the cell j′ of thereconfigurable antenna k′.

T_(uncov)[(k,j) (k′,j′)] will denote the uncovered traffic in the spacebetween the cell j of the reconfigurable antenna k and the cell j′ ofthe reconfigurable antenna k′.

In the specific example represented in FIG. 9, the following applies:

T_(superp)[(1,1)(2,1)] will denote the superposition traffic between thecell 1 of the antenna 1 and the cell 1 of the antenna 2;

T_(superp)[(3,1)(1,1)] will denote the superposition traffic between thecell 1 of the antenna 3 and the cell 1 of the antenna 1;

T_(uncov)[(2,1)(3,1)] will denote the uncovered traffic associated tothe intercell space that separates the cell 1 of the antenna 2 and thecell 1 of the antenna 3.

The process for managing superpositions or overlaps (i.e. the step 202of FIG. 4) is activated downstream of the cell construction step 200whatever the number (e.g. 1 to 4) of cells assigned to the antenna ofthe site. The step 202 has the object of removing possibleoverlaps/superpositions among the cells.

The superposition management process starts from the superpositionhaving the higher superposition traffic associated therewith.

FIG. 6 exemplifies the presence of a single cell for each of the threeantennas in the site, by assuming that the following condition is met:

T _(superp)[(1,1)(2,1)]>T _(superp)[(3,1)(1,1)]

The superposition [(1,1)(2,1)] is thus considered first. For each of theoverlapping cells, i.e. (1,1) and (2,1) the non-superposed traffic(generally denoted T_(non-superp), while the same formalism describedabove for the superposition traffic is adopted for the cell indexes) iscalculated. This is obtained by subtracting the superposition trafficfrom the traffic offered to the cell:

T _(non-superp)(1,1)=T(1,1)−T _(superp)[(1,1)(2,1)]

T _(non-superp)(2,1)=T(2,1)−T _(superp)[(1,1)(2,1)]

The cell having the lowest non-superposed traffic acquires theelementary sector having superposed traffic that is most internal to it(i.e. closest to the angular direction of the “mechanical” azimuth) andthe associated traffic adds to the non-superposed traffic of the samecell. Downstream of such acquisition, the values for the non-superposedtraffic for the cells are again determined to identify again the cellhaving the smallest amount of non-superposed traffic. Such a cell willthen be assigned the innermost sector therein.

This process is continued until no superposed elementary sectors remain,so that the superposition is removed. The process is repeated in aniterative manner by considering each and every superposition that ispresent.

FIG. 10 exemplifies a site configuration obtained as a result ofmanaging the superpositions shown in FIG. 9:

the superposition [(1,1)(2,1)] has been managed by attributing one ofthe two elementary sectors to the cell (1,1) and the other in the cell(2,1);

the superposition [(3,1)(1,1)] has been managed by attributing thesingle overlapping elementary sector overlap to the cell (3,1).

The step 204, devoted to managing the intercell spaces has the object ofremoving with intercell spaces, i.e. the areas found to be uncovered.

The step 204 starts by managing the intercell space to which thehigher/highest value of uncovered traffic is associated and involves,for each intercell space, the following phases:

i) the two adjacent cells are examined to identify the cell having thelower value of offered traffic (it will be appreciated that, as a resultof the step 202, the site configuration no longer includessuperpositions);

ii) the cell so identified is checked to see whether it can acquire theneighboring elementary sector (which belongs to the intercell spacebeing examined) without violating any of the conditions on the maximumamplitude, the azimuth or the target traffic T_(target) consideredpreviously;

iii) the process loops back to phase i) and proceeds in an iterativemanner by analyzing the remaining unassigned sectors until assignment iscompleted or all the cells have reached their limits of expansion interms of number of sectors or maximum traffic.

If, downstream of these phases, the intercell spaces are completelyeliminated (positive outcome of a step 206), the process is terminatedand the cells of the reconfigurable site are defined (in number andamplitude, that is in terms of the number of elementary angular sectorsof its own competence).

Conversely, if unassigned elementary sectors still exist (negativeoutcome of a step 206), the reconfigurable antenna that manages themaximum value of traffic (obtained by adding the traffic levels of thecells associated therewith) is found and a check is made as to whetherit is still possible to increase the number of cells.

In the positive case, in a step 208, the system increases the number ofcells and loops back to the cell construction step 200. The process isiterated until the intercellar spaces are completely eliminated.

In the negative case, i.e. if the number of cells cannot be increasedsince the maximum number (for instance 4) has already been reached, theelementary sectors not yet assigned are attributed to the adjacent cellseven if such attribution exceeds the load limits for these cells.

The various operations just described are exemplified in FIGS. 10 and11, where—out of the three elementary sectors belonging to the intercellspace [(2,1)(3,1)], one is acquired by the cell (2,1), one is acquiredby the cell (3,1) and one remains uncovered. As a result, the number ofcells associated to the reconfigurable antenna 2 (to which sixelementary sectors are attributed in the configuration of FIG. 11) isincreased from 1 to 2. The new sector partitioning, where two cells areassigned to the reconfigurable antenna 2, is schematized in FIG. 12.

Even if this event is not expressly catered for in the precedingdescription, case may occur where (either before or after thesuperpositions are removed) no uncovered areas are revealed. In thatcase, the optimization process may involve reducing the number of cellsand checking whether the desired coverage may be achieved with a smallernumber of cells.

The optimization process described herein proceeds (step 104 of FIG. 1)with the definition of the optimum diagram in the vertical plane (V) foreach of the cells previously identified. In the vertical plane V anapproach can be adopted which is thoroughly similar to the approachadopted in the horizontal plane H (i.e. by using a mask). In a preferredembodiment, a radiation diagram is considered in the vertical planedefined as a diagram equivalent to the diagram that would be defined byhypothesizing the presence of a single 3 dB lobe having a width α_(3dB)with a tilt angle such as to maintain the 3 dB lobe confined within adistance equal to the highest value R(j) among the maximum distances(i.e. the pixels farthest away from the site) associated to theelementary sectors included in the cell j being considered.

Given a cell identified by a certain number of elementary sectors, theoptimum electrical tilt (i.e. the tilt obtained by exploiting thereconfigurable nature of the antenna) is calculated via the followingrelationship:

${\theta (j)} = {{{arc}\; {\tan \left( \frac{{h_{BTS}(j)} - {h_{UE}(j)}}{R(j)} \right)}} + \frac{\alpha_{3\mspace{11mu} {dB}}}{2}}$

where:

h_(BTS)(j) is the altitude (over sea level) of the reconfigurableantenna associated with the cell;

h_(UE)(j) is a reference altitude (over sea level) for the generic userto be served by the cell: such a reference altitude can determined as afunction of the average altitude in the cell and the average height ofthe buildings therein, both calculated on the pixels belonging to theelementary sectors in included in the cell;

R(j) is the value defined in the foregoing;

α_(3dB)/2 is the half-amplitude of the vertical lobe of the diagram Vconsidered (independent from the value of tilt); the value for α_(3dB)is determined from the number of elements of the array along thevertical axis on the basis of criteria that are well known to theseexperts of the sector.

The meaning of the parameters discussed above is illustrated in FIG. 13.

Subsequently, the optimization process generally represented in the flowchart of FIG. 1 proceeds with a step 106 devoted to the definition ofthe optimum diagram on the horizontal plane (“H diagram”).

The optimization process described so far defines the angular amplitudesof the radiation diagrams on the horizontal plane, which are coherentwith the angular amplitudes of the cells. Reconfigurable antennas dohowever offer a higher degree of flexibility, in that they also permitan optimization of the angular distribution of the energy radiatedwithin each cell. This can be achieved by properly defining the shape ofthe H diagram.

The procedure for defining the H diagram the construction of a “cellmask” starting from the values of the representative attenuations of thevarious elementary sectors and from the distribution of the offeredtraffic. The cell mask is defined on the basis of the followingprocedure:

a weight p_(i) is calculated for each elementary sector by consideringthe values of traffic and representative attenuation associated with therelated sector on the basis of the following relationship:

$p_{i} = {\frac{A_{i}^{rap}}{\max\limits_{l \in j}\left( A_{l}^{rap} \right)} + \frac{T_{i}}{\max\limits_{l \in j}\left( T_{l} \right)}}$

where j denotes the cell that contains the sector i, A^(rap) _(i)denotes the value of the representative attenuation for the sector i,expressed on a linear scale, while T_(i) is the traffic offered to thesector overall. In calculating the weight p_(i), the two quantities arenormalized by dividing them by the maximum representative attenuationand by the maximum traffic, respectively, as evaluated over the sectorsbelonging to the cell;

for each cell, two vectors having elements (φ_(i), m_(i)) areconstructed having dimensions equal to the number of elementary sectorsthat comprise the cell, where the elements φ_(i) correspond to theangular direction of the axis of the elementary sector while theelements m_(i) are calculated according to the following relationship:

$m_{i} = \left\{ \begin{matrix}\frac{p_{i}}{\max\limits_{l \in j}\left( p_{l} \right)} & {{if}\mspace{14mu} {the}\mspace{14mu} {elementary}\mspace{14mu} {sector}\mspace{14mu} i\mspace{14mu} {belongs}\mspace{14mu} {to}\mspace{14mu} {the}\mspace{14mu} {cell}\mspace{14mu} j} \\0 & {otherwise}\end{matrix} \right.$

In practice, the vector so built contains values selected between 0 and1 that, insofar as the elementary sectors belonging to the cell areconcerned, correspond to the values of the weights calculated previouslyand subsequently normalized with reference to the maximum value of theweights of each cell;

the cell mask is formally represented by a vector of e.g. 721 elements(corresponding to a discretization of the angle of 360 degrees intosteps of 0.5 degrees). The values of the elements of this vector aredefined by interpolating the values derived from the vector constructedat the previous step that has a resolution equal to the amplitude of theelementary sector (typically 5°). In a preferred embodiment, a thirddegree polynomial interpolation is used, of a known type.

The meaning of the parameters discussed above is illustrated in FIG. 14.FIG. 15 reproduces some exemplary cell masks associated to a siteincluding three sectors or cells. In the example shown, the three arrayantennas (reconfigurable antennas) have mechanical azimuth values of 10,130 and 270 degrees, respectively.

According to the general system layout illustrated, by way ofnon-limiting example in FIG. 16, the optimization process describedherein lends itself to being carried out automatically by means of acomputer program loaded into a computer 10.

In a particularly preferred embodiment, described in the following, theoutput of the optimization process described herein is essentiallycomprised of the following entities, defined for each reconfigurableantenna:

number of activated cells Ok;

tilt of each of the activated cells H_(k,j);

horizontal diagram (H), described by the cell mask H_(k,j) for each ofthe activated cells (for instance discretized as a vector of 721elements).

This information is transferred from the computer 10 to the controlserver 20 of e.g. a mobile telecommunication network. Such a server istypically present in all mobile telecommunication networks to centralizethe basic control functions of the network. These consist, e.g., of: 1)monitoring performance indicators (for instance the total powertransmitted from the cell) and alarms made available by the differentnetwork apparatuses (adapted, for instance, to identify failure ormalfunctioning); 2) dispatching towards network apparatus commands withthe object of modifying the operational criteria of this apparatus:these commands include for instance commands sent to the RET (RemoteElectrical Tilt) equipment installed on the antennas of the radio basestations in order to modify (by acting from the server 10) the pointingof these antenna.

The information needed for reconfiguring the antennas associated withthe different cells are sent from the server 20 towards the various basestations 30 that in turn forward this information over channels 40adapted to carry this information (generally designated 50) towardscontrol units 60 associated with the antennas 70. In a preferredembodiment, the information 50 is conveyed in the form of commandstransmitted in binary format and in transparent way over digitalconnections extending between the server 20 and the radio base stations30 and between the radio base stations and the control units 60 of thereconfigurable antennas 70. In a preferred embodiment, a separatecommand is transmitted for each reconfigurable antenna.

Together with the information on the diagrams provided as an output bythe optimisation process, the server 10 can send towards the antennasadditional information/commands to control the power to be assigned tothe pilot channels of the various cells. Specifically, this command istransmitted at least when the optimization process leads to a change inthe number of cells associated to an antenna.

The information derived from the algorithm process can be transportedwithin the command 50 in different ways or modes. Three of these aregiven as a non-limiting example.

Mode 1: on the basis of antenna synthesis techniques of a known type(see e.g. R. J. Mailloux “Phased Array Antenna Handbook” 2nd Edition,Artech House, 2005 pages 109-121) a program installed in the computer 10translates the information on the tilt and on the horizontal diagramprovided by the optimization process into corresponding configurationsof weights to be sent to the different elements of the array thatconstitutes the antenna. For each antenna k, Q_(k)×N_(k)×M_(k) complexweights are computed, where N_(k) and M_(k) correspond to the dimensionsof the (plane) array, while Q_(k) represents the number of cellsactivated the antenna. The complex weights so calculated are convertedinto binary numbers and transferred to the server 20 according todigital techniques of a known type. In the server 20 the weights areincluded in a control command to be sent to the control unit 60. Thecontrol unit 60 in turn sends to each of the some N_(k)×M_(k) elementsthat comprise the reconfigurable antenna 70 the Q_(k) sets of weightsthat define the antenna diagram for each of the Q_(k) cells that areactivated.

Mode 2: the outputs of the optimization process (number of activatedcells, value of tilt for each cell, horizontal diagram (H), properlydiscretized for each cell) are transferred by the computer 10 to theserver 20 and from here on to the control unit 60 in the form of acommand 50. For each activated cell, the control unit 60 synthesizes thecomplex weights to be allotted to the elements of the array andtransmits to each element in the antenna array 70 the correspondingweight. This occurs on the basis of known techniques analogous to thoseused in Mode 1 as previously described.

Mode 3: the computer 10 and the control unit 60 contain databases forpossible antenna diagrams. For each type of reconfigurable antenna, adifferent database is present. By way of non-limiting example one mayconsider the simple case where all the reconfigurable antennas are ofthe same type. In this case, the database will have the followingstructure:

[i]

[complex weights (i)]

[H_(i)][t_(i)]

Each index in the database identifies a configuration of complex weightsthat defines a diagram H_(i) (described by a vector of e.g. 721elements) and a value of tilt t_(i). For each reconfigurable antenna kand for each cell j activated in the antenna k, a program installed inthe computer 10 performs a correlation among the cell mask H_(i,k)provided as an output by the optimization process and the diagrams H_(i)present in the database. Such procedure allows to calculate, for each ofthe diagrams H_(i), a coefficient of correlation C_(i), for instance onthe base of the following relationship:

$C_{i} = \frac{{cov}\left( {H_{j,k},H_{i}} \right)}{\sqrt{{{cov}\left( {H_{j,k},H_{j,k}} \right)} \cdot {{cov}\left( {H_{i},H_{i}} \right)}}}$

where the function cov(X,Y) it is defined by the following relationship:

cov(X,Y)=E{[X−E(X)]·[Y−E(Y)]}

and the function E{X}, applied to a vector of e.g. 721 elements, each ofwhich denoted by x_(i), corresponds to the following relationship:

${E\left\{ X \right\}} = {\frac{1}{721}{\sum\limits_{l = 1}^{721}x_{l}}}$

The coefficient C_(i) with the highest value corresponds to the diagramH_(i), out of those included in the database, which is most similar tothe cell mask. If different indexes exist (for instance i and i′)corresponding to identical diagrams H_(i) and H_(r), the systemidentifies the index corresponding to a tilt value which is closer tothe tilt value provided by the optimization process, namely t_(j,k). Inthat way, the process identifies the index corresponding to the pair[H_(i)] [t_(i)] that is more similar to the one identified by theoptimisation process. Typically, a specific index i is identified foreach cell j, while however the same diagram with an index can beassociated with different cells. The Q_(k) indexes so identified foreach reconfigurable antenna k are transferred by the computer 10 to theserver 20 and from this on to the control unit 60 of the antenna 70,through a command 50. By resorting to a database similar to thatincluded in the computer 10, the control unit 60 identifies the Q_(k)sets of complex weights corresponding to the Q_(k) values included inthe command 50 and sends them to the elements in the antenna array 70.

Consequently, without prejudice to the underlying principles of theinvention, the details and the embodiments may vary, even appreciably,with reference to what has been described by way of example only,without departing from the scope of the invention as defined by theannexed claims.

1-20. (canceled)
 21. A method for configuring an antenna site equippedwith at least one reconfigurable antenna in a communication network,said antenna site having capacity to serve communication traffic in arespective area of competence, comprising the steps of: partitioningsaid area of competence in a reference set of cells; and evenlydistributing said communication traffic among said cells in said set foroptimizing the number of cells in said set, said step of evenlydistributing said communication traffic among said cells comprising thesteps of: a) checking said set of cells to locate: i) areas ofsuperposition between adjacent cells, wherein said areas ofsuperposition correspond to areas covered jointly by traffic capacity ofadjacent cells in said set of cells, and ii) uncovered areas betweenadjacent cells, wherein said uncovered areas correspond to areas notcovered by traffic capacity of any cell in said set of cells; b)removing said areas of superposition whereby traffic capacity is madeavailable from either of the adjacent cells that gave rise tosuperposition; c) assigning to said uncovered areas said trafficcapacity made available by removing said areas of superposition; and d)if any uncovered areas remain, increasing the number of cells in saidreference set of cells, and repeating steps a) to d) above.
 22. Themethod of claim 21, wherein if no uncovered areas between adjacent cellsare located, comprising the steps of decreasing the number of cells insaid reference set of cells, and repeating steps a) to d) above.
 23. Themethod of claim 21, wherein said step of removing said areas ofsuperposition is started from cells in said reference set of cellsgiving rise to superposition and having associated therewith a highertraffic level.
 24. The method of claim 21, wherein said step of removingsaid areas of superposition comprises the step of at least partlyassigning coverage of said areas of superposition to one, of saidadjacent cells having associated therewith a lower traffic level. 25.The method of claim 21, wherein said assigning to said uncovered areassaid traffic capacity made available is started from uncovered areashaving associated therewith a highest level of traffic left uncovered.26. The method of claim 21, wherein said assigning to said uncoveredareas said traffic capacity made available comprises the step of atleast partly assigning coverage of said uncovered areas to the one ofsaid adjacent cells having associated therewith a lower traffic level.27. The method of claim 21, wherein said increasing the number of cellsin said reference set of cells if any uncovered areas remain, comprisessplitting into two a cell in said reference set of cells havingassociated therewith a highest traffic level in the set.
 28. The methodof claim 21, comprising the step of determining an area of competence asa set of pixels satisfying the following requirements: a field receivedat the pixel from an isotropic antenna equipping said antenna site ishigher than fields received from cells associated with other sites inthe communication network; and the field received at the pixel from saidisotropic antenna equipping said antenna site is higher than a minimumthreshold.
 29. The method of claim 21, comprising the steps of:partitioning an area of competence into elementary sectors of constantangular amplitude in a horizontal plane; and aggregating said elementarysectors to form said cells.
 30. The method of claim 29, wherein saidelementary sectors have an angular amplitude of 5 to 20 degrees.
 31. Themethod of claim 29, wherein said elementary sectors have an angularamplitude which is a submultiple of 360°.
 32. The method of claim 28,comprising the step of determining communication traffic associated withsaid cells and any elementary sectors thereof by adding trafficassociated with the pixels belonging thereto.
 33. The method of claim21, wherein said step of evenly distributing said communication trafficamong said cells in said set comprises checking communication trafficassociated with each cell in said set against a maximum value oftraffic.
 34. The method of claim 21, wherein said step of evenlydistributing said communication traffic among said cells in said setcomprises checking each cell in said set against at least one of: anangular width of the cell reaching a maximum value; and the cellreaching a maximum angular distance from a mechanical azimuth of theantenna.
 35. The method of claim 21, comprising the step of associatingwith an optimized number of cells, a respective radiation diagram ofsaid reconfigurable antenna in at least one of a vertical and ahorizontal plane.
 36. A system for configuring an antenna site equippedwith at least one reconfigurable antenna in a communication network,said antenna site having capacity to offer communication traffic in arespective area of competence and having associated therewith a controlunit to control the configuration of said at least one reconfigurableantenna, comprising at least one computer configured for performing themethod of claim 21, and capable of sending to said control unit, antennaconfiguration commands corresponding to results of said method.
 37. Thesystem of claim 36, wherein said at least one computer configured forconverting said results into configuration data of a radiation diagramof said at least one reconfigurable antenna and sending saidconfiguration data toward said control unit.
 38. The system of claim 36,wherein said at least one computer is configured for sending saidresults toward said control unit and said control unit is configured forconverting said results into configuration data of a radiation diagramof said at least one reconfigurable antenna.
 39. The system of claim 36,wherein: said at least one computer and said control unit haverespective databases for storing possible radiation diagrams of said atleast one reconfigurable antenna; said at least one computer isconfigured for identifying in a database, as a function of said results,a given possible radiation diagram of said at least one reconfigurableantenna and sending toward said control unit a corresponding index; andsaid control unit is configured for identifying in its database, as afunction of said index, a given possible radiation diagram of said atleast one reconfigurable antenna and configuring said at least onereconfigurable antenna according to said given possible radiationdiagram.
 40. A communication network comprising an antenna site equippedwith at least one reconfigurable antenna, said antenna site havingcapacity to serve communication traffic in a respective area ofcompetence and having associated therewith a control unit to control theconfiguration of said at least one reconfigurable antenna, wherein saidcontrol unit is adapted to reconfigure said at least one reconfigurableantenna using results generated by the method of claim 21.